Enable 'set print inferior-events' and improve detach/fork/kill/exit messages

Enable 'set print inferior-events' and improve detach/fork/kill/exit messages

This patch aims to turn 'set print inferior-events' always on, and do
some cleanup on the messages printed by GDB when various inferior
events happen (attach, detach, fork, kill, exit).

To make sure that the patch is correct, I've tested it with a handful
of combinations of 'set follow-fork-mode', 'set detach-on-fork' and
'set print inferior-events'.  In the end, I decided to make my
hand-made test into an official testcase.  More on that below.

Using the following program as an example:

  #include <unistd.h>
  int main ()
  {
    fork ();
    return 0;
  }

We see the following outputs from the patched GDB:

- With 'set print inferior-events on':

    (gdb) r
    Starting program: a.out
    [Detaching after fork from child process 27749]
    [Inferior 1 (process 27745) exited normally]
    (gdb)

- With 'set print inferior-events off':

    (gdb) r
    Starting program: a.out
    [Inferior 1 (process 27823) exited normally]
    (gdb)

  Comparing this against an unpatched GDB:

- With 'set print inferior-events off' and 'set follow-fork-mode
  child':

    (gdb) r
    Starting program: a.out
    [Inferior 2 (process 5993) exited normally]
    (gdb)

  Compare this against an unpatched GDB:

    (unpatched-gdb) r
    Starting program: a.out
    [New process 5702]
    [Inferior 2 (process 5702) exited normally]
    (unpatched-gdb)

  It is possible to notice that, in this scenario, the patched GDB
  will lose the '[New process %d]' message.

- With 'set print inferior-events on', 'set follow-fork-mode child'
  and 'set detach-on-fork on':

    (gdb) r
    Starting program: a.out
    [Attaching after process 27905 fork to child process 27909]
    [New inferior 2 (process 27909)]
    [Detaching after fork from parent process 27905]
    [Inferior 1 (process 27905) detached]
    [Inferior 2 (process 27909) exited normally]
    (gdb)

  Compare this output with an unpatched GDB, using the same settings:

    (unpatched-gdb) r
    Starting program: a.out
    [New inferior 28033]
    [Inferior 28029 detached]
    [New process 28033]
    [Inferior 2 (process 28033) exited normally]
    [Inferior 28033 exited]
    (unpatched-gdb)

As can be seen above, I've also made a few modifications to messages
that are printed when 'set print inferior-events' is on.  For example,
a few of the messages did not contain the '[' and ']' as
prefix/suffix, which led to a few inconsistencies like:

  Attaching after process 22995 fork to child process 22999.
  [New inferior 22999]
  Detaching after fork from child process 22999.
  [Inferior 22995 detached]
  [Inferior 2 (process 22999) exited normally]

So I took the opportunity and included the square brackets where
applicable.  I have also made the existing messages more uniform, by
always printing "Inferior %d (process %d)..." where applicable.  This
makes it easier to identify the inferior number and the PID number
from the messages.

As suggested by Pedro, the "[Inferior %d exited]" message from
'exit_inferior' has been removed, because it got duplicated when
'inferior-events' is on.  I'm also using the
'add_{thread,inferior}_silent' versions (instead of their verbose
counterparts) on some locations, also to avoid duplicated messages.
For example, a patched GDB with 'set print inferior-events on', 'set
detach-on-fork on' and 'set follow-fork-mode child', but using
'add_thread', would print:

  (gdb) run
  Starting program: a.out
  [Attaching after process 25088 fork to child process 25092.]
  [New inferior 25092]   <--- duplicated
  [Detaching after fork from child process 25092.]
  [Inferior 25088 detached]
  [New process 25092]    <--- duplicated
  [Inferior 2 (process 25092) exited normally]

But if we use 'add_thread_silent' (with the same configuration as
before):

  (gdb) run
  Starting program: a.out
  [Attaching after process 31606 fork to child process 31610]
  [New inferior 2 (process 31610)]
  [Detaching after fork from parent process 31606]
  [Inferior 1 (process 31606) detached]
  [Inferior 2 (process 31610) exited normally]

As for the tests, the configuration options being exercised are:

- follow-fork-mode: child/parent
- detach-on-fork: on/off
- print inferior-events: on/off

It was also necessary to perform adjustments on several testcases,
because the expected messages changed considerably.

Built and regtested on BuildBot, without regressions.

gdb/ChangeLog:
2018-04-24  Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Sergio Durigan Junior  <sergiodj@redhat.com>
	    Pedro Alves  <palves@redhat.com>

	* infcmd.c (kill_command): Print message when inferior has
	been killed.
	* inferior.c (print_inferior_events): Remove 'static'.  Set as
	'1'.
	(add_inferior): Improve message printed when
	'print_inferior_events' is on.
	(exit_inferior): Remove message printed when
	'print_inferior_events' is on.
	(detach_inferior): Improve message printed when
	'print_inferior_events' is on.
	(initialize_inferiors): Use 'add_inferior_silent' to set
	'current_inferior_'.
	* inferior.h (print_inferior_events): Declare here as
	'extern'.
	* infrun.c (follow_fork_inferior): Print '[Attaching...]' or
	'[Detaching...]' messages when 'print_inferior_events' is on.
	Use 'add_thread_silent' instead of 'add_thread'.  Add '[' and ']'
	as prefix/suffix for messages.  Remove periods.  Fix erroneous
	'Detaching after fork from child...', replace it by '... from
	parent...'.
	(handle_vfork_child_exec_or_exit): Add '[' and ']' as
	prefix/suffix when printing 'Detaching...' messages.  Print
	them when 'print_inferior_events' is on.
	* remote.c (remote_detach_1): Print message when detaching
	from inferior and '!is_fork_parent'.

gdb/testsuite/ChangeLog:
2018-04-24  Jan Kratochvil  <jan.kratochvil@redhat.com>
	    Sergio Durigan Junior  <sergiodj@redhat.com>
	    Pedro Alves  <palves@redhat.com>

	* gdb.base/attach-non-pgrp-leader.exp: Adjust 'Detaching...'
	regexps to expect for '[Inferior ... detached]' as well.
	* gdb.base/attach.exp: Likewise.
	* gdb.base/catch-syscall.exp (check_for_program_end): Adjust
	"gdb_continue_to_end".
	(test_catch_syscall_with_wrong_args): Likewise.
	* gdb.base/foll-fork.exp: Adjust regexps to match '[' and
	']'.  Don't set 'verbose' on.
	* gdb.base/foll-vfork.exp: Likewise.
	* gdb.base/fork-print-inferior-events.c: New file.
	* gdb.base/fork-print-inferior-events.exp: New file.
	* gdb.base/hook-stop.exp: Adjust regexps to expect for new
	'[Inferior ... has been killed]' message.
	* gdb.base/kill-after-signal.exp: Likewise.
	* gdb.base/solib-overlap.exp: Adjust regexps to expect for new
	detach message.
	* gdb.threads/kill.exp: Adjust regexps to expect for new kill
	message.
	* gdb.threads/clone-attach-detach.exp: Adjust 'Detaching...'
	regexps to expect for '[Inferior ... detached]' as well.
	* gdb.threads/process-dies-while-detaching.exp: Likewise.